Magnetic pulleys of the type contemplated herein are used to separate or sort ferrous metal pieces from scrap material travelling on a conveyor belt. Typical separators of this type are disclosed in U.S. Pat. No. 4,869,811, issued to Richard B. Wolanski, et al., on Sep. 26, 1989, entitled "Rotor For Magnetically Sorting Different Materials," U.S. Pat. No. 3,448,857, issued to William H. Benson, et al., on Jun. 10, 1969, entitled "Electrodynamic Separator," and U.S. Pat. No. 3,454,913, issued to Arlo F. Israelson, et al., on Jul. 8, 1969, entitled "Permanent Magnetic Pulley." Each of these patents discloses a magnetic pulley wherein a number of rows of magnets are arranged in spaced relation on the rotor to produce alternating magnetic polarity flux fields.
In the U.S. Pat. No. '857 and U.S. Pat. No. '811 patents, the magnets are mounted on the outer periphery of a cylindrical rotor and held in position by nonmagnetic shells. In the U.S. Pat. No. '913 patent the magnets are shown mounted on an octagon shaped rotor and held in place by a nonmagnetic shell. In each of these patents the magnets are aligned axially with each alternate row of magnets having opposite polarity. In separators of this type a mixture of discrete parts or particles with various electrical conductivity characteristics are projected through an intense unidirectional field with the line of motion of the particles essentially at 90.degree. with the direction of the field, whereby particles of greater conductivity will be decelerated to a greater extent than those of lesser conductivity with the result that different kinds of particles will have different trajectories in emerging from the field and separation of the particles will thereby be achieved.
By rapidly rotating the pulley, a bandlike zone of rapidly reversing high density magnetic flux is produced along the length of the pulley. The pulley is supported horizontally to provide a narrow bandlike area above the pulley, through which the ferrous and nonferrous pieces are moved. As each piece passes through the zone it is momentarily subjected to an alternating magnetic flux which induces an eddy current within the piece. This eddy current in turn produces a repulsive magnetic force in the piece which repels the piece from the zone. By moving the piece through the zone upon a horizontal conveyor which ends at the zone the repulsive force causes the piece to freely continue moving along a trajectory whose length will vary depending upon the strength of the repulsive force. This strength is correlated to the particular type of metal of which the piece is formed, thus the distance which the piece moves away from the zone is proportional to the kind of metal out of which the piece is made, therefore different metals are separated by the distances which the individual pieces travel from the zone.